mql5/Experts/_Architecture/Events/EventBus/EventBus.mqh

//+------------------------------------------------------------------+
//|                                                     EventBus.mqh |
//|                                  Copyright 2025, MetaQuotes Ltd. |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2025, MetaQuotes Ltd."
#property link      "https://www.mql5.com"
#property version   "1.00"

#include "AbstractEvent.mqh"
#include "IEventListener.mqh"

//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
class EventBus
  {
private:
   // Subscription record
   struct Subscription
     {
      EventType       type;
      IEventListener* listener;
     };

   // Circular buffer for event pointers
   AbstractEvent*      m_queue[512];
   int               m_head;
   int               m_tail;

   // Dynamic array of subscriptions
   Subscription      m_subscriptions[];
   int               m_subCount;

   // Find index of a specific subscription, or -1
   int               FindSubscription(EventType type, IEventListener* listener) const
     {
      for(int i = 0; i < m_subCount; i++)
        {
         if(m_subscriptions[i].type == type && m_subscriptions[i].listener == listener)
            return i;
        }
      return -1;
     }

public:
                     EventBus() : m_head(0), m_tail(0), m_subCount(0) {}

   // Subscribe a listener for a specific event type
   void              Subscribe(EventType type, IEventListener* listener)
     {
      if(FindSubscription(type, listener) >= 0)
         return;   // already subscribed

      int size = ArraySize(m_subscriptions);
      ArrayResize(m_subscriptions, size + 1);
      m_subscriptions[size].type     = type;
      m_subscriptions[size].listener = listener;
      m_subCount = size + 1;
     }

   // Unsubscribe
   void              Unsubscribe(EventType type, IEventListener* listener)
     {
      int idx = FindSubscription(type, listener);
      if(idx < 0)
         return;

      // Shift remaining elements
      for(int i = idx; i < m_subCount - 1; i++)
         m_subscriptions[i] = m_subscriptions[i + 1];
      m_subCount--;
      ArrayResize(m_subscriptions, m_subCount);
     }

   bool              IsEmpty() const { return m_head == m_tail; }
   bool              IsFull()  const { return ((m_tail + 1) % 512) == m_head; }

   // Push an event (takes ownership of the pointer)
   void              Push(AbstractEvent* event)
     {
      if(IsFull())
        {

         delete event;
         return;
        }

      m_queue[m_tail] = event;
      m_tail = (m_tail + 1) % 512;
     }
   void              Dispatch()
     {
      while(!IsEmpty())
        {
         AbstractEvent* event = m_queue[m_head];
         m_head = (m_head + 1) % 512;
         EventType type = event.GetType();
        

         int matchCount = 0;
         for(int i = 0; i < m_subCount; i++)
           {
            if(m_subscriptions[i].type == type)
              {
               matchCount++;
               m_subscriptions[i].listener.OnEvent(event);
              }
           }
 
         delete event;
        }
     }
      
   // Clean up any remaining events (e.g., on shutdown)
   void              Clear()
     {
      while(!IsEmpty())
        {
         AbstractEvent* event = m_queue[m_head];
         m_head = (m_head + 1) % 512;
         delete event;
        }
     }

                    ~EventBus()
     {
      Clear();
     }
  };
//+------------------------------------------------------------------+
//+------------------------------------------------------------------+